A toilet’s rough-in is the distance from the finished wall behind it to the center of the drain, which is where the two floor bolts sit. 12 in is the standard and the most common size; 10 in and 14 in toilets are made for the rest. Measure from the wall itself, not the baseboard, shortlist toilets made for your number or a size down, and check the model’s spec sheet before you buy.
How to measure a toilet rough-in
- Find the bolts. The two caps at the base of the toilet cover the bolts that hold it to the drain flange. With four caps, use the back pair.
- Measure from the wall. Run the tape from the finished wall surface, the drywall or tile, to the center of a bolt. Measuring from the baseboard reads short by its thickness.
- Round to the size. About 10, 12 or 14 in is your rough-in. A reading a little over, like 12½ in, still takes a 12 in toilet, which then stands ½ in farther from the wall than its drawing shows.
10, 12 and 14 inch rough-ins compared
| Rough-in | How common | Example toilet | Wall to bowl front |
|---|---|---|---|
| 10 in | Less common | Kohler Cimarron K-3851, round front | About 28½ in |
| 12 in | The most common | TOTO Drake CST744S; Mansfield Alto 135-160 | About 28¾ to 29½ in |
| 14 in | Less common | Mansfield Alto 135-125 | 31½ in |
Depths from the makers’ spec sheets (see the sources); the 10 in Kohler and 12 in TOTO figures add the gap behind the tank to the toilet’s length. A toilet one size smaller than your rough-in goes on about 2 in farther from the wall than its drawing shows, which takes 2 in from the floor in front; one size larger won’t go on as drawn.
If the drain is in the wrong place for the toilet you want, a plumber can fit an offset flange, which moves the toilet up to 2 in (Oatey). Moving the drain itself is a bigger job, and it’s plumber’s work under a permit.
The space a toilet needs
The 2021 International Residential Code wants at least 15 in from the toilet’s centerline to a wall, a partition, a vanity or another fixture on each side, and at least 21 in of clear floor in front. Designers aim for 18 in and 30 in. For whole-room layouts, try the layout planner; for the sizes of the toilets themselves, see toilet dimensions.
Questions people ask
What is a toilet rough-in?
The distance from the finished wall behind the toilet to the center of its drain, which is where the floor bolts are. It decides which toilets fit: 10, 12 or 14 in models.
What is the standard toilet rough-in?
12 in, the size American Standard calls the most common.
Can I put a 12 in rough-in toilet on a 10 in rough-in?
No: its tank would hit the wall. Use a toilet made for 10 in, or ask a plumber about an offset flange.
Can I put a 10 in rough-in toilet on a 12 in rough-in?
Yes. It stands about 2 in farther from the wall than its drawing shows, so check that the floor in front still has 21 in clear.
Do I measure from the baseboard or the wall?
The wall. Kohler’s roughing-in sheet asks for the full 12 in to be clear from the wall or the baseboard to the drain’s center, and says to trim a baseboard that cuts into it.
Sources
- How to measure: American Standard: how to measure for a replacement toilet (from the bolts’ center to the wall, not the baseboard; 10, 12 and 14 in), TOTO Drake II installation manual and Kohler K-3654 roughing-in sheet
- Toilet spec sheets: Kohler Cimarron K-3851 (10 in), TOTO Drake CST744S (12 in), Mansfield Alto 135-160 (12 in) and 135-125 (14 in)
- Oatey: should I use an offset toilet flange? (up to 2 in in any direction)
- 2021 International Residential Code, chapter 3 (R307.1 fixture clearances, R305.1 ceiling height) and chapter 27 (P2705.1 fixture spacing, P2708.1 showers), read in Colorado’s adoption without amendments on UpCodes
- Larimer County, Colorado: Figure R307.1 bathroom clearances
- NKBA’s free bath planning guidelines: the roomier spacing (18 in beside a toilet, 20 in beside a sink, 36 in between two sinks, 30 in in front of each fixture, a 36 × 36 in shower, a 32 in door opening, a 36 × 66 in toilet compartment). Its newer, paid editions change some numbers.
Checked October 30, 2026.